1. Field of the Invention
The present invention relates to an optical axis aligning method for aligning the respective optical axes of an optical component and an optical fiber with speed, accuracy, and ease, in connecting the component and the fiber, and an apparatus therefor.
2. Related Art
In constructing optical devices that include optical elements such as light emitting elements, light receiving elements, optical switches, optical modulators, etc., an optical fiber is connected to another optical fiber or an optical element (hereinafter an optical fiber and an optical element connected to an optical fiber will be collectively referred to as an optical component). In connecting the optical fiber and the optical component, their respective optical axes are aligned with each other, that is, optical axis alignment is carried out.
For example, in connecting the optical fiber with an LD module that includes a laser diode (hereinafter referred to as xe2x80x9cLDxe2x80x9d) element, for use as a light emitting element, and a lens for converging-light emitted from the LD element, it is necessary to align the point of emission on a connecting end face of the LD module and the center of an incidence end face of the optical fiber and align the direction of emission from the LD module and the longitudinal axis of the optical fiber. In other words, the LD module and the optical fiber must be relatively positioned with respect to the X-, Y-, and Z-axes, if a plane that is parallel to the connecting end face of the LD module and the direction perpendicular to the plane are defined as an XY-plane and the Z-axis direction, respectively. The optical axis alignment requires particularly high accuracy when the optical component and the optical fiber are to be connected fixedly, as in the case of joining an LD module and a ferruled optical fiber by YAG welding.
Conventionally, in the optical axis alignment of this type, the quantity of light emitted from an optical component such as an LD module and incident upon a connecting end face of an optical fiber is measured by means of an optical power meter that is connected to the other end of the fiber, as the optical component and the optical fiber are relatively three-dimensionally moved, to thereby find out a relative position (optimum relative position) for a maximum light quantity.
In order to find out the optimum relative position of the optical component and the optical fiber in an XYZ-space with high accuracy, according to the conventional method described above, light quantity measurement should be made at a large number of relative positions in the XYZ-space, so that the optical axis alignment requires much time and labor. In case the longitudinal axis (optical axis) of the optical fiber is deviated from the Z-axis, in particular, the optimum relative positions in the X- and Y-axis directions shift as the relative position in the Z-axis direction varies, so that the optimum relative position in the XYZ-space cannot be found out with ease. Thus, the optimum relative position in the XYZ-space must be obtained by repeatedly measuring the light quantity while changing the relative positions in the X- and Y-axis directions every time the relative position in the Z-axis direction is changed.
If the number of points of light quantity measurement (relative positioning points involving light quantity measurement) is not good enough, local optimum values alone may be determined in the case where the light quantity distribution of the light emitted from the optical component is not represented by a unimodal function. In this case, the position for the maximum light quantity cannot be found out.
Although the problems on the optical axis alignment between a light emitting element and an optical fiber have been described above, the optical axis alignment between an optical fiber and a light receiving element or between optical fibers involves the same problems.
The object of the present invention is to provide an optical axis aligning method for an optical component and an apparatus therefor, capable of aligning the respective optical axes of the optical component and an optical fiber with speed, accuracy, and ease.
According to one aspect of the present invention, there is provided an optical axis aligning method for an optical component, in which the quantity of light emitted from an optical component or an optical fiber and incident upon the other is measured as the optical component and the optical fiber are positioned successively in a plurality of relative positions, to thereby obtain an optimum relative position for a maximum light quantity. This method comprises a step (a) of subjecting light quantity distribution on a given plane parallel to a connecting end face of the optical component or the optical fiber to quadric surface approximation in accordance with measured light quantities at a plurality of points on the given plane, thereby obtaining an optimum point on the given plane and a step (b) of subjecting light quantity distribution in the direction of the optical axis of the optical component or the optical fiber or in the direction of a given axis perpendicular to the given plane to quadratic function approximation in accordance with measured light quantities at a plurality of points in the direction of the optical axis or the given axis, thereby obtaining an optimum point in the direction of the optical axis or the given axis.
According to the conventional method, in optical axis alignment prior to the connection between an optical component and an optical fiber, a maximum light quantity point (optimum relative position) is searched for as the optical component and the optical fiber are successively relatively positioned at a large number of points in a three-dimensional space (XYZ-space). In other words, the optical component and the optical fiber are relatively positioned in the X-, Y-, and Z-axis directions at the same time.
In the optical axis aligning method of the present invention, the determination of the optimum point on the given plane (XY-plane) based on the quadric surface approximation of the light quantity distribution on the XY-plane and the determination of the optimum point in the direction of the optical axis or the given axis (Z-axis) based on the quadric function approximation of the light quantity distribution in the optical axis direction or the Z-axis direction are carried out independently of each other, so that, in accordance with the optimum point on the XY-plane and the optimum point in the optical axis direction or the Z-axis direction, the optimum relative position in the XYZ-space can be determined more speedily and easily than in the case of the conventional method. Further, optimum relative positions (optimum points) on the XY-plane and in the Z-axis direction can be accurately obtained by the quadric surface approximation and the quadric function approximation, so that the optimum relative position in the XYZ can be obtained accurately. The optimum relative position on the XY-plane and the optimum relative position in the Z-axis direction are represented by X-, Y-, and Z-coordinate values of a target position of the optical component or the optical fiber, for example. More generally, these positions are represented by two sets of X-, Y-, and Z-coordinate values that are indicative of the respective target relative positions of the optical component and the optical fiber.
Preferably, the step (a) includes a sub-step (a11) for subjecting light quantity distribution in the direction of a first axis, defining the given plane, to quadric function approximation in accordance with measured light quantities at a plurality of points in the first axis direction, a sub-step (a12) for subjecting light quantity distribution in the direction of a second axis, defining the given plane in conjunction with the first axis, to quadric function approximation in accordance with measured light quantities at a plurality of points in the second axis direction, and a sub-step (a13) for obtaining the optimum point on the given plane according to the quadric function approximation of the light quantity distribution in the first axis direction and the quadric function approximation of the light quantity distribution in the second axis direction.
According to this preferred method, the quadric surface approximation on the given plane can be carried out relatively easily, and the optimum relative position of the optical component and the optical fiber can be obtained with ease. Further, the accuracy of determination of the optimum point can be improved by increasing the numbers of measurement points in the first and second axis directions, and labor and time required by the determination of the optimum point can be reduced by lessening the measurement points in number. For example, measurement points in each of the first and second axis directions may be three. Moreover, one of the measurement points in the first axis direction may be used as one of the measurement points in the second axis direction so that the number of measurement points can be reduced.
Further preferably, the step (a) includes a sub-step (a14) for determining the optimum point on the given plane when the optimum point on the given plane is converged near a given one of the points in the first and second axis directions, and a sub-step (a15) for updating the setup of the points in the first and second axis directions and rerunning the sub-steps (a1) and (a2) when the optimum point on the given plane is not determined.
According to this preferred method, in determining the optimum point on the given plane by the quadric surface approximation, the required accuracy for the determination of the optimum point on the given plane is previously set in the form of an allowable value, so that the optimum point can be determined speedily and with the required accuracy.
Alternatively, the step (a) includes a sub-step (a21) for solving simultaneous equations obtained by substituting the measured light quantities at the points on the given plane individually into polynomial approximate expressions representing the light quantities on the given plane as functions of position coordinates on the given plane, thereby obtaining unknown coefficients of the respective terms of the polynomial approximate expressions, a sub-step (a22) for measuring the light quantity at the optimum point on the given plane obtained in the sub-step (a13), a sub-step (a23) for substituting the position coordinates of the optimum point on the given plane into the polynomial approximate expressions having the coefficients determined in the sub-step (a21), thereby obtaining an arithmetic value of the light quantity at the optimum point on the given plane, a sub-step (a24) for determining the optimum point on the given plane when the light quantity measured in the sub-step (a22) is converged near the arithmetic value obtained in the sub-step (a23), and a sub-step (a25) for updating the setup of the points in the first and second axis directions and rerunning the sub-steps (a1) and (a2) when the optimum point is not determined.
According to this preferred method, the obtained optimum point is accurate because it is determined when the difference between the measured light quantity at the optimum point, obtained by the quadric surface approximation, on the given plane and the arithmetic value of the light quantity at the optimum point is within its allowable range.
Preferably, the step (a) includes subjecting light quantity distributions on two given planes with different given axial positions to quadric surface approximation, thereby searching for the optical axis direction, and the step (b) includes subjecting light quantity distribution in the searched optical axis direction to quadric function approximation in accordance with measured light quantities at a plurality of points in the searched optical axis direction.
According to this preferred method, the optical axis direction is searched for according to the light quantity distributions on the two given planes, and the optimum point in the optical axis direction corresponding to the optimum relative position in the XYZ-space can be obtained with speed, accuracy, and ease from the light quantity distribution in the optical axis direction.
According to the preferred method described above, optimum points on the two given planes are individually obtained by the quadric surface approximation of the light quantity distributions on the two planes in the step (a), and the optimum point in the direction of the given axis is obtained by the quadric function approximation of the light quantity distribution in the given axis direction in the step (b), for example. Optimum point deviations in the directions of the two axes that define the given plane are obtained from the optimum points on the two given planes, and the optimum relative position of the optical component and the optical fiber is obtained according to the optimum point in the given axis direction, the two optimum point deviations, and the optimum point on at least one of the given planes. In the case of this example, the optimum point deviations in the respective directions (X- and Y-axis directions) of the two axes that define the given plane are obtained from the results of light quantity measurement on the two given planes that have different given axis direction positions, and the optimum point in the given axis direction (Z-axis direction) is obtained thereafter. Then, the optimum point on the XY-plane for the optimum position in the Z-axis direction is obtained according to the optimum point deviations and the optimum point on the one given plane. Thus, light quantity measurement need not be made to obtain the optimum point on the XY-plane every time the optical component and the optical fiber are relatively moved in the Z-axis direction, so that the optimum relative position in the XYZ-space can be obtained speedily and accurately. A straight line that connect the optimum points on the two given planes having the different Z-axis direction positions corresponds to the optical axis of the optical component or the optical fiber, so that a search for the optimum point in the Z-axis direction that involves the correction of the optimum point on the XY-plane based on the optimum point deviations is equivalent to a search for the optimum point in the optical axis direction. Thus, even in the case of obtaining the optimum point in the Z-axis direction while relatively moving the optical component and the optical fiber in the Z-axis direction with the component and the fiber supported in a manner such that the optical axis of the component or the fiber deviated from the given axis (Z-axis) perpendicular to the given plane (XY-plane) that extends parallel to the connecting face of the component or the fiber, the optimum point in the optical axis direction can be obtained speedily and accurately if the optimum point on the XY-plane having the Z-axis direction position concerned is corrected by means of the optimum point deviations after the optimum point in the Z-axis direction is determined.
An optical axis aligning method according to another aspect of the invention comprises a step (a) of obtaining an optimum point on a given plane parallel to a connecting end face of an optical component or an optical fiber by the simplex method in accordance with measured light quantities at a plurality of points on the given plane and a step (b) of subjecting light quantity distribution in the direction of the optical axis of the optical component or the optical fiber or in the direction of a given axis perpendicular to the given plane to quadric function approximation in accordance with measured light quantities at a plurality of points in the direction of the optical axis or the given axis, thereby obtaining an optimum point in the direction of the optical axis or the given axis.
According to the present invention, the optimum point (maximum light quantity point) on the given plane is obtained by using the simplex method. According to the simplex method, the maximum light quantity point can be satisfactorily obtained even in case the light quantity distribution of the light emitted from the optical component is not represented by a unimodal function or if it cannot be appropriately represented by quadric function approximation.
Preferably, according to the invention, the step (a) includes a sub-step (a11) for selecting a minimum light quantity point for a minimum light quantity, among a required number of first set points on the given plane, in accordance with measured light quantities at the first set points and selecting two other first set points than the minimum light quantity point, a sub-step (a12) for setting a required number of second set points on a straight line extending from the minimum light quantity point to the side opposite from the minimum light quantity point and passing through the middle point of a segment connecting the two first set points and selecting a maximum light quantity point for a maximum light quantity, out of the second set points, in accordance with measured light quantities at the second set points, a sub-step (a13) for selecting the maximum light quantity point as a new first set point in place of the minimum light quantity point, a sub-step (a14) for obtaining the newly selected first set point as an optimum point on the given plane when the respective lengths of segments connecting the adjacent new first set points are smaller than a maximum allowable value, and a sub-step (a15) for rerunning the sub-steps (a1) and (a2) when the respective lengths of the segments are not smaller than the maximum allowable value.
This preferred method is a concrete form of the simplex method that is used to determine the optimum point on the given plane. In this method, new set points for larger light quantities are repeatedly set in place of a minimum light quantity point, among other set points on the given plane. By doing this, a polygonal region that connects the set points is converged near the maximum light quantity point as it is shifted to the higher-light side on the given plane. Thus, according to this preferred method, the optimum point (maximum light quantity point) on the given plane can be obtained speedily and accurately.
Further preferably, the sub-step (a11) includes setting three of the first set points on the given plane, and said sub-step (a12) includes setting one second set point between the minimum light quantity point and the middle point of a segment connecting the remaining two first set point, on a straight line extending from the minimum light quantity point and passing through the middle point, and setting two second set points on the side remote from the minimum light quantity point with respect to the middle point.
According to this preferred method, the number of set points is minimized so that the optimum point on the given plane can be obtained more speedily and easily.
Preferably, the step (a) includes obtaining optimum points on two given planes with different given axial positions, thereby determining the optical axis direction, and the step (b) includes subjecting light quantity distribution in the determined optical axis direction to quadric function approximation in accordance with measured light quantities at a plurality of points in the determined optical axis direction.
According to this preferred method, the optimum point in the optical axis direction corresponding to the optimum relative position in the XYZ-space can be obtained speedily and accurately by the quadric function approximation of the light quantity distribution in the optical axis direction. Even if a determination of the optimum point in the Z-axis direction is made with the optical axis of the optical component or the optical fiber deviated from the given axis (Z-axis), the optimum point in the optical axis direction can be obtained with speed and accuracy, equivalently.
According to still another aspect of the invention, there is provided an optical axis aligning apparatus for an optical component, in which the quantity of light emitted from the optical component or an optical fiber and incident upon the other is measured as the optical component and the optical fiber are positioned successively in a plurality of relative positions, to thereby obtain an optimum relative position for a maximum light quantity. This optical axis aligning apparatus comprises a first stage movable along a first axis, a second stage supporting the optical component or the optical fiber and supported on the first stage for movement along a second axis perpendicular to the first axis, a third stage supporting the optical fiber or the optical component and movable along a third axis perpendicular to the first and second axes, a light quantity measurer for measuring the quantity of light emitted from the optical component or the optical fiber and incident upon the other, and an arithmetic drive unit for obtaining an optimum point on a given plane defined by the first and second axes by the simplex method or by quadric surface approximation of light quantity distribution on the given plane, in accordance with measured light quantities at a plurality of points on the given plane, obtaining an optimum point in the direction of the third axis by quadric function approximation of light quantity distribution in the direction of the third axis, in accordance with measured light quantities at a plurality of points in the direction of the third axis, and suitably driving the first, second, and third stages so that the optical component and the optical fiber are relatively positioned on the optimum points on the given plane and in the direction of the third axis.
In the optical axis aligning apparatus of the invention, the arithmetic drive unit obtains the optimum point on the given plane by the simplex method or by the quadric surface approximation of the light quantity distribution on the given plane (XY-plane), and obtains the optimum point in the direction of the third axis by the quadric function approximation of the light quantity distribution in the direction of the third axis (Z-axis direction), so that the optimum relative position in the XYZ-space can be obtained speedily and accurately. The first, second, and third stages of the optical axis aligning apparatus are driven to position the optical component and the optical fiber in the optimum relative position, whereby the optical axis alignment is completed.
Preferably, the arithmetic drive unit obtains optimum points on two given planes with different third-axis-direction positions and deviations between optimum points in the first and second axis directions, and corrects the optimum point on the given plane with the optimum point deviations as the third stage moves in the direction of the third axis.
According to this preferred apparatus, the optimum point on the given plane (XY-plane) having the Z-axis direction position corresponding to the optimum point in the third axis direction (Z-axis direction) is obtained according to the optimum point deviations and the optimum point on the one given plane, so that the optimum relative position in the XYZ-space can be obtained speedily and accurately.
According to the present invention, the respective optical axes of an optical fiber and various optical elements, such as light emitting elements, light receiving elements, etc., and those of optical fibers can be aligned with one another with speed, accuracy, and ease.